Tennon and recess size

[Raif Harik]

Guess I can't edit the title with that typo

Hi, I wondering what the optimal size was for tenons and recesses in relation to chuck jaws I guess I always heard a tenon should be as small as the jaws allow. But for recesses I've heard both large as possible and small as possible.
Any thoughts?
Thanks,
R

 

[Curt Fuller]

The jaws on your chuck are adjustable but the optimum holding power is when they are at or near the perfectly round position. That gives you the most contact with the wood. There are a lot of variables but when you open them too much for either a tenon or a recess you reach a point where only the edges of the jaws are contacting the tenon or the center of the jaws are contacting the recess. Equally as important is a good flat shoulder with a tenon so the face of the jaws has full contact and a flat bottom for a recess for the same reason. If you're finding that you're not comfortable with the size of the tenon or recess it's time for a larger set of jaws and/or a larger chuck rather than pushing the limits of the jaws by opening them too far.
That said, although there are times when a recess works, I think a tenon is almost always the better route.

 

[David Hill]

What Curtis says....
I use both tenons and recesses-- for me it just depends on what the wood says. My routine is to cut a channel that will allow either a tenon or recess to be used once the outside is shaped. Generally I work toward a bottom that is at least 1/3 the diameter of the bowl. It just depends on the wood. A recess requires good structural integrity in the blank---which is sometimes problematic in my favorite wood--Mesquite.
Although I now have a vacuum chuck that may change how I look at some blanks.

 

[hockenbery]

Guess I can't edit the title with that typo

Hi, I wondering what the optimal size was for tenons and recesses in relation to chuck jaws I guess I always heard a tenon should be as small as the jaws allow. But for recesses I've heard both large as possible and small as possible.
Any thoughts?
Thanks,
R

the optimum hold on a tenon is a true circle size of the jaws. This is about 1/8” gap between the jaws.
This is no good on a greenwood bowl that will shrink when it dries.

#2 jaws on my vicmarc are at true circle when closed to 48mm About 1.9”

when I rough turn a bowl for drying I use a tenon 2.5” diameter. When the bowl dries I can always turn a 2” diameter tenon from the dried oval tenon.

Th dovetail jaws when closing to close to full circle do not leave a perceptible mark.
I can grip an ornament or a ball with a 48 mm groove cut into it and not leave a mark.

 

[Paul M. Kaplowitz]

Tenon and recess - 40% of the diameter.

 

[John Torchick]

Good article to ponder. Got a piece of wood on the lathe turned to round. Debating putting it in a Supernova 2 chuck, faceplate, or using a glue block. Read somewhere that the more closed the jaws, the better the grip. What about a big blank? I like Paul's answer. With a bowl that big, Paul, you would want the best grip!
My jaws open to 45 mm (1-13/16) and the turning is four inches in diameter. 4 X 40% is 1.6 inches (a hair under 1-5/8) which would put it in Paul's recommendations.
Thanks to all from a semi-professional maker of shavings and sawdust.

 

[Arkriver]

The whole issue of proper chucking seems to be a never ending learning process. Take a look at Doc Greens web site. It is a great one and answers all sorts of turning questions. His book is also a good one. There is no easy one size fits all answer. Allyn

 

[Mike Johnson]

A recess works great for platters, dishes and bowls that you do not want to remount after turning and finishing is complete. If you can turn, sand and finish the recess side of the project it is quick and easy to turn the inside profile, sand and finish the item and you are done. The tenon mounting usually requires an extra step in tenon removal and final finishing. Removing the tenon can sometimes lead to the piece coming off the lathe if you get in a hurry and get a catch while removing the tenon. It happens to everyone.

 

[John Torchick]

Thinking of a tenon, finishing the outside and inside with a bowl gouge. Reversing and putting on Cole jaws. Your thoughts? Needtot justify the cost of the CJs.

 

[Forrest Forschmiedt]

I love my cole jaws! It can be a bit tedious to move the 8 rubber nibs for different sized bowls but worth it.
I bought mine in a set from Rockler with a G3 chuck and the standard 50mm jaws. It came with long jaw screws so you can actually mount both the cole jaws and smaller 50mm jaws at the same time. After turning the inside of your bowl you can flip it around and remove the tennon without changing jaws or chucks.

 

[hockenbery]

Thinking of a tenon, finishing the outside and inside with a bowl gouge. Reversing and putting on Cole jaws. Your thoughts? Needtot justify the cost of the CJs.

Regardless of how you turn off the tenon be sure you know how thick the bottom is.

save your money ...
It is relatively easy to learn to reverse Chuck a bowl over a rounded block of wood with a paper towel pad.
Then shape the interior of the foot turn away the tenon.

I used Cole jaws for a while but now use reverse chucking most of the time because is so quick easy and positive. I rarely use my vacuum chuck because jamb chucking work so well.

Cole jaws work but tend to be too restrictive on the rim design and take too long to set up.
They Don’t work for Natural edge bowls.

Returning a dried bowl video is part of a demo I do on turning bowls from wet wood.
You can fast forward to 32:40 to see how I measure the bottom
Fast forward 36:09 to see finish turning the bottom

View: http://www.youtube.com/watch?v=sCZWsHB4vlM

To see the whole process including turning a bowl to dry take a look at the returning a dry bowl video in this thread to see how the reverse chucking works.
http://aawforum.org/community/index.php?threads/working-with-green-wood.11626/

 

[Russell Nugent]

Tenon diameter being 40% may be a thing but I don't think that's a good idea to max out your jaws to get there. Im assuming you're talking 40 percent of the base diameter. That's why they make larger jaws. Im a big proponent of keeping the tenon to the point where your jaws are a circle, except as pointed ot above that doesn't really work for green turning. I have 2", 3" and 4" jaws.

I use coke jaws when I have a bunch of smaller bowls to finish the bottoms on. One offs, once turned etc I just friction drive like Al and then chisel and sand the nub.
Hopefully something I've said makes sense, since there has to be a first time.

 

[Dean Center]

Thinking of a tenon, finishing the outside and inside with a bowl gouge. Reversing and putting on Cole jaws. Your thoughts? Needtot justify the cost of the CJs.

John, The Thrifty Woodworkers Union strongly recommends a book by the name of "The Frugal Woodturner" by Ernie Conover. Unsurprisingly, he details a great many ways to accomplish things that might appear to require purchasing more gear. It includes half a dozen DIY ways to hold bowl blanks and nearly finsished bowls, though not how to make your own Longworth chuck, which is an equivalent of the Cole jaws. The Longworth tutorial can be found online, including possibly on the AAW website somewhere. Maybe your local club library has a copy of Ernie's book you could borrow.

 

[John Torchick]

I have looked at a couple of YT videos, Mike Peace included, and Lyle Jameison's video on bowl turning. I'm considering to start on a glue block. Then using the parted off material as a jam chuck to finish the bottom. Lots of ways to accomplish the same thing.
Again, many thanks for the replies. Will go back and review them.
Edit- Dean, is thrifty the same as cheap? I'm so cheap, they have my picture next to the word in the dictionary!

 

[Roger Wiegand]

I recently learned a neat trick for reverse chucking-- you can buy silicone hotpads at any kitchen supply place or amazon for a couple bucks each. They have a little give to them, I just put one over the end of my chuck and then bring the workpiece up and hold with the tailstock. The steel chuck doesn't mar the work through the hot pad, the silicone rubber grabs both the steel and wood so nothing slips, and you don't have to change fixtures or turn a wooden block.

To make life with Cole jaws easier I recently got some hex (allen) drives that fit my impact driver. It makes getting the jaws on and off the chuck and moving the rubber bumpers about 10 faster and less irritating.

All that said, I recently acquired a vacuum chucking system, and it is heavenly to use!

 

[hockenbery]

Lyle's glueblock method works great. I use it if I don’t have the 1/2” of wood to give up for the tenon.

I consider it a more advanced method than just using a tenon on the blank because of the increased complexity
Have to turn the coves on the glueblock face and the bowl blank face then line them up

If you do use it one trick is to twist the glueblock slightly as it contacts the beads of glue. This spreads out the CA into nice wide bonding surface filling the space between the two coves. Just sliding the glue block down the Alignment rod can let the glue harden as a bead with the result having little holding surface.

 

[Rob Price]

I’ll second the vacuum chuck- IF you spend money I would put it in a vacuum chuck vs buying cole jaws or a longs worth chuck. And there’s a guy selling ‘frugal’ vacuum chuck systems out there. I bought some commercial vacuum chucks but my homemade PVC and craft foam chucks I built myself are 10x better. They aren’t perfect but I do a lot of natural edge bowls and the other solutions won’t work.

Another option is a donut chuck. I do have a big donut chuck I started working on but never finished it. I need to- for the times my vacuum chuck won’t hold.

 

[John Torchick]

Don't have the funds for a vacuum chuck. Besides, I hear they really suck!!!!

 

[Tom Gall]

I love my cole jaws! It can be a bit tedious to move the 8 rubber nibs for different sized bowls but worth it.
I bought mine in a set from Rockler with a G3 chuck and the standard 50mm jaws. It came with long jaw screws so you can actually mount both the cole jaws and smaller 50mm jaws at the same time. After turning the inside of your bowl you can flip it around and remove the tennon without changing jaws or chucks.

I never liked Cole or Jumbo jaws for many reasons - ranging from safety to convenience. Are you familiar with “flat jaws” (available for many brands of chucks)? Turn your Cole jaws into a large set of Flat jaws. Remove all the screws and rubber bumpers and replace with four pieces of soft wood, MDF, PVC foam board (or whatever) to each of the pie shaped jaws and attach with screws from the back side. Doesn’t have to be pretty…just close. Open the jaws a little (or more) ….. cut a groove to the approximate diameter and width of your bowl rim (can be straight in or dovetailed depending on your bowl rim shape) ….. mount bowl rim in groove and tighten jaws slightly.

Advantages: 1) works in both contraction and expansion modes for different types of bowl rims. 2) almost 100% contact with the rim. 3) automatically centers the bowl. 4) can be used many, many times over for different size bowls. Need a new spot?....expand or contract jaws to an unused area and cut a new groove. 5) easily replaced when totally used up. 6) safer and more convenient.

Best to use the tailstock for safety until the final cuts …..then sand without obstruction from the tailstock. After all that……I still prefer my vacuum chuck!

 

[John Torchick]

Tom, how about a photo?

 

[Dean Center]

Dean, is thrifty the same as cheap? I'm so cheap, they have my picture next to the word in the dictionary!

You and I are charter members of the Thrifty Rod Builders Union, so I assumed you were also invited to be a member of the Thrifty Woodturners Union. Thrifty is a euphemism for cheap--they mean the same thing but thrifty is less likely to give offense. I thought all you Southern boys learned such things along with your molasses manners at Mama's knee?

 

[John Torchick]

Actually, I'm from Ohio. I'm what is called a DXXX Yankee, that is, I came down South and stayed! A Yankee comes South for a short while and goes back up North. We moved to the Atlanta area in 1965. A neighbor said he was 17 years old before he discovered damyankee was two words!

 

[Tom Gall]

Tom, how about a photo?

John….. I’m somewhat technologically inadequate. That is why I’ve never posted a Gallery photo on this site or any other that I visit. I don’t have a smart phone ….. so I would have to take my camera to the shop to take a photo(s) – remove the memory card – install on my computer – download to my Photos program ….. THEN figure out how to resize them and post them to the forum!

I seem to recall doing this once several years ago but don’t remember the process, … but, I do remember that it took me quite a bit of time and effort!

I was hoping that you could visualize the chuck from my description.
That said, maybe I’ll try the process again if I get a chance in the next day or so.

 

[John Torchick]

I recently learned a neat trick for reverse chucking-- you can buy silicone hotpads at any kitchen supply place or amazon for a couple bucks each. They have a little give to them, I just put one over the end of my chuck and then bring the workpiece up and hold with the tailstock. The steel chuck doesn't mar the work through the hot pad, the silicone rubber grabs both the steel and wood so nothing slips, and you don't have to change fixtures or turn a wooden block.

To make life with Cole jaws easier I recently got some hex (allen) drives that fit my impact driver. It makes getting the jaws on and off the chuck and moving the rubber bumpers about 10 faster and less irritating.

All that said, I recently acquired a vacuum chucking system, and it is heavenly to use!

Roger, I have some foam padding that I might try. Put two layers of masking tape on the jaws and expanded inside the turning. Left a mark so I had to hit it with the side scraper. Live and learn.

 

[John Torchick]

Tom, know what you mean by technologically hindered. FWIW, I have an Android (Verizon) phone. Take photo> start computer> attach a USB cable to the phone> insert USB connector to USB port in laptop> downloads the photo. Unhook and view the photo on the Pictures files.
Memory card reader,Kodak A-250, 50-in-one Card Reader. I take the memory card from the camera, insert into the appropriate slot in the reader, insert into the USB port. Downloads automatically.
So easy, even I can do it! And I'm not a caveman.

 

[Raif Harik]

@Arkriver That article by doc green is pretty good he seems to disagree with most of the answers on here. Probably why you pointed to the article rather than call it out . He says the largest possible tenon and recess are best unless you have a longer(deeper) piece. He has lots of logic and reasoning for this position in the article. It's pretty convincing. I'd be interested in what others think of that article.
http://www.docgreenwoodturner.com/holdingpower1.html

 

[Raif Harik]

Regarding cole jaws, reverse chucking etc. I have a had time getting my bowl centered on a reverse chuck block. I have the spot for the tailstock but the chuck has no reference on the inside of the bowl. Unless I create a chuckblock for each bowl. I put a piece of foam over a waste block and stick it inside the bowl, then it's a total crap shoot as to whether it's centerd.
R

 

[hockenbery]

Regarding cole jaws, reverse chucking etc. I have a had time getting my bowl centered on a reverse chuck block. I have the spot for the tailstock but the chuck has no reference on the inside of the bowl. Unless I create a chuckblock for each bowl. I put a piece of foam over a waste block and stick it inside the bowl, then it's a total crap shoot as to whether it's centerd.
R

Centering a Reverse chucked piece can be frustrating in the beginning. With experience it just happens.

for reversing a once turned bowl or the second turning of a twice turned bowl it do three things that make the reverse chucking centering easy.

1 leave the center point from the tail stock in the tenon when I turn the tenon. when I reverse it the tenon is centered using the center point in the tenon and the bowl will be close to centered.

2. The jamb chuck piece that goes inside the bowl is a turned round with a slight concave. I test this for true running every time I use it and true it if needed. This makes a circular edge to contact a curving inside of the bowl.
This makes the reverse chucking center up most of the time.

3 I use a paper towel as a pad. This is one layer of thin paper that does not affect the centering. A spongy type pad will often push the bowl bowl off center and resist attempts at moving to center.

after lightly tightening the tailstock I check the bowl for running true. By putting my thumb on the toool rest close to the bowl. Most of thime it will be running true. If nit there there is one side that hits my thumb and it is off center toward that side. I put that side straight up, hold the bowl, loosen the tailstock slightly, and keeping the tail center engaged with the tenon let the bowl shift downward on the jamb Chuck. This will usually gets it on center in two or three tries. Once in a while it takes longer especially if I overshoot how much to move it.

if I am recentering a warped dried bow that is a process where I line up the warped part of the rims. I still use a centerpoint left in the tenon. You can see this process in the video

View: http://www.youtube.com/watch?v=sCZWsHB4vlM

 

[Raif Harik]

@hockenbery
So two things come to mind. 1 is that the foam I'm using is pretty think and kind of bunches up so perhaps thats adding to my sufferning. 2. my jam block doesn't always touch the sides of the bowl. Sometimes just the edge. Someone did mention just using the chuck as the jam block and I imagine that would not generally touch the sides either. So maybe that's not an issue.
Thanks,
R

 

[hockenbery]

Someone did mention just using the chuck as the jam block

I use the chuck as the jamb block only when I am returning a a dried bow as the metal will mark the bowl.

My reverse chuck block is little wider than the tenon. When I reverse chuck I’m pressing the bottom center of the bowl against the rim of the jamb chuck block. Sort of wood sandwich with a paper towel in between.

This is my jamb chuck block below. I use this on on bowls up to 15-16” diameter.

 

[Rob Price]

@Arkriver That article by doc green is pretty good he seems to disagree with most of the answers on here. Probably why you pointed to the article rather than call it out . He says the largest possible tenon and recess are best unless you have a longer(deeper) piece. He has lots of logic and reasoning for this position in the article. It's pretty convincing. I'd be interested in what others think of that article.
http://www.docgreenwoodturner.com/holdingpower1.html

That’s a great article and a good explanation of the physics of the tenon. What it means to me is that as long as I’m not at the extremes (large or small) of the tenon size I’m in good shape- assuming I’m using appropriate jaw size for the piece. I do get nervous at max tenon size that the corners of the jaws aren’t supported by enough wood behind them- that the tenon could blow out at those corners. It also explains why folks can use a larger tenon during roughing to allow for warping and don’t have issues.

For my own turning, the actual shaping of the dovetail tenon has affected the gripping power more than size. After watching a few videos of Stuart Batty and Ashley Harwood explaining how a slightly undercut shoulder, where the chuck jaws extend just past the shoulder, provides maximum contact with the face of the jaws and shoulder of the tenon my tenons have been much stronger and more accurate to the point where I rarely have to do any re-shaping of the outside when I flip a bowl around for hollowing. I also knock off the corner of the dovetail to avoid the situation doc green talks about if the shape is too acute. A few mm difference in the shape of the tenon have way more effect on its performance than a few mm on the size of the tenon.

With the emphasis on good shoulder contact I’ve also quit using my stock Nova 50mm jaws for bowls- they just don’t have a wide enough face- I always get runout. I started using the 35mm spigot jaws- they have a face width closer to the other bowl jaws, and even with a smaller tenon I get a more accurate re-mounting. I do stay well within the 5x limit he talks about. I’m quick to move up to larger jaws as needed.

 

[Roger Wiegand]

If I think about chuck failures I've had the number of times the work has slipped in the chuck are in the low single digits. The much more common failure mode is for the tenon to shear off the piece or the edge of the recess to break from over-expansion of the chuck. That tells me that for me keeping the tenon as large as possible or the wall surrounding the recess as thick as possible are the most important things to do to prevent failures. Having the wood slip in the chuck is too rare an occurrence to even bother thinking about

 

[Mike Johnson]

Assuming the recess and tenon profiles are done correctly to start with.

 

[Roger Wiegand]

I'm not very fussy about tenon shape, I do make sure I have a good flat for the chuck to rest against and that it doesn't bottom out in the chuck. I don't obsess over matching the angle of the tenon to the dovetail shape of the chuck, anything 90 deg or less seems to be fine. The corners of the chuck jaws dig in a little and seem to hold quite tenaciously.